\documentclass[11pt]{article}

\begin{document}
$1+(2+3)$
\begin{theorem}
$5+4$
$5*4$
$1+(2*(3+4)+5)*6+7*8$
\end{theorem}
$$(34+(8+6))$$
$555%5=0$
$1.6/x>8$
\end{document}